The main objective of this proposal is to investigate by direct measurement how individual mitral neurons are functionally organized and incorporate the results in a compartmental model of the mitral nerve cell. The long-term goal is to use the information about individual nerve cells as the basis for an understanding of how networks of interconnected neurons operate to control behavior. In the long run, the knowledge we obtain about how normal behavior is generated will help us understand mental disorders such as depression, drug addiction or schizophrenia. Understanding how single neurons process information is fundamental to understanding how the brain works. A complete understanding of any individual cell's function has not yet been obtained. Due to linear and nonlinear membranes, the regional electrical properties of branching processes are complex and impossible to predict in the absence of spatially resolved measurements. The experiments will be carried out to characterize in detail one exemplar neuron, the mitral neuron in the rat olfactory bulb. We will try to look at the processing of excitatory (from olfactory nerve) and inhibitory inputs (from granule cells), in the most direct way, by optical monitoring of membrane potential transients at many sites by using intracellular voltage sensitive dyes. We plan to determine the number and locations of trigger zones and to determine whether dendrites are capable of generating spikes. We are going to test experimentally the hypothesis that besides the apical (primary) dendrite the back propagation, also occurs in tuft and secondary dendrites to influence synaptic plasticity. We also plan to test the hypothesis that individual neurons can be functionally subdivided. If true, this postulate would have important implications for the functional complexity of individual neurons.